1. Field of Invention
The present invention relates to an antenna and, in particular, to a dual-band antenna.
2. Related Art
The vigorous development of the wireless transmission brings various kinds of applications for multi-band transmission products and technology, so that many new products have the function of wireless transmission to satisfy the consumers' needs. An antenna is the very important element for transmitting and receiving the electromagnetic wave energy in the wireless transmission system. Without it, the wireless transmission system will not be able to transmit and receive data. A proper antenna may not only match the appearance of the product and enhance the properties of transmission, and also further reduce the product cost.
The common band protocols are such as the Wi-Fi (IEEE 802.11) and Bluetooth (IEEE 802.15.1) communication. Bluetooth devices operate within 2.4 GHz band. The 802.11 also includes 802.11a 802.11b, 802.11g, and 802.11n that are specifically defined for the 5 GHz band and 2.4 GHz band.
However, each country has a different open band especially for IEEE 802.11a. The components for IEEE 802.11a must adapt to different band ranges, for example, a high band (5.47 to 5.725 GHz) is needed to support an output of 1 W in European countries for fitting in every channel. Also, the band range of the common dual-band antenna can only cover a part of the range; hence the operating range of the product is limited under the band regulations in different countries. Thus, the application products of the dipole antenna cannot be used in every country.
Additionally, the frequency band allocation of WiMax (IEEE 802.16) that each country has been gradually opened on still does not have a global standard. In each country, only the licensed frequency band can be used for WiMax. For example, a frequency band from 2.3 GHz to 2.4 GHz is used for WiMax in Korea, and three WiMax licenses have been issued there. A frequency band from 2.5 GHz to 2.7 GHz that is used for WiMax in the U.S., Canada, Singapore, and Israel is categorized as the U.S. regulation. A frequency band from 3.4 GHz to 3.6 GHz that is used for WiMax in China and European countries is categorized as the European regulation. Therefore, the application products of the dipole antenna need to fit into the different regulations in different countries.
According to the above, one of the important subjects is to increase the operating band range of the dual-band antenna so that the application products of the dual-band antenna can fit into the regulations of more countries.